Low mileage in itself is not a concern to me, and indeed I would always prefer it to high mileage.
If the low mileage is because the unit sat without proper maintenance for a long period of time, that is a problem. It's not the low mileage, but the lack of maintenance. I would check any used unit as carefully as I could, particularly with regards to caulking and water intrusion.
Do be aware that some parts (particularly rubber things like hoses and bushings and tires) degrade over time as well as with use. Don't be surprised if you need some repairs at "only" low mileage due to the age of the parts. There are those who assert that use is better for mechanical systems than moderate periods of disuse, but I don't see how that works out in practice--it just sometimes seems that way because the parts wear out (due to age) "sooner" than expected, but not actually sooner than if they were used more. That's my impression/opinion.
Do plan on getting new tires quite soon, perhaps immediately, unless they have been replaced already.